1. Field of the Invention
The present invention relates to a storage apparatus and a method for managing the storage apparatus.
2. Related Background Art
Data stored in storage apparatuses used in computer systems is periodically stored on magnetic tapes as backup data, so that data lost due to apparatus failure or operation error can be recovered. Backup data, in addition to being stored as backup, is used as data for batch processing and/or test data for application programs.
It is important that the backup data thus utilized is data of a specific point in time and that this can be guaranteed. When a part of data is updated during a backup processing, the data loses consistency.
A processing to obtain backup data involves repeating data copy processing, which requires a long time. The loss of data consistency can be prevented by halting all processing other than the backup processing, thereby preventing any data from being updated; however, a suspension of any processing for long periods of time cannot be allowed on systems that perform online processing.
Mirroring is known as a technology to obtain backup data (first technology). Mirroring is a technology to physically duplicate volumes within a storage apparatus. A copy processing is conducted in order to achieve consistency of data between the volumes. When data is updated during the copy processing, data in both of the volumes are updated. Backup data is obtained in this way according to a mirroring technique.
According to another known method to obtain backup data, when data is updated during a backup processing, data to be updated is saved in a different region before the data is actually updated (second technology). In the backup processing, the saved data can be backed up instead of the updated data.
Another method to obtain backup data is a method in which, in addition to volumes containing data to be backed up (primary volumes), virtual auxiliary volumes having a primary-secondary relation with the primary volumes are provided, such that when data in the primary volumes is updated during a backup processing, the data to be updated is saved in the auxiliary volumes (third technology). The backup processing for the updated data is the same as in the second technology.
The marked difference among the technologies described above is that, while the point at which copy generation is completed and thereafter is considered the specific point in time according to the first technology, the point at which data save begins is considered the specific point in time according to the second and third technologies.
Data of a certain point in time such as backup data is called frozen image data, or simply a frozen image. Frozen images are also sometimes called snapshots. In addition to being stored as backup data, frozen images are used in application programs such as batch processing programs. Such application programs must sometimes be executed during the execution of online programs, and generating frozen images is an extremely important task especially in computer systems that operate 24 hours a day.
In such usage environment for computer systems, the first technology requires time for copying data that cannot be allowed on such computer systems, as described above. Furthermore, due to the fact that obtaining and using frozen images according to the first technology are limited to at or after copy generation is completed, there are limitations in selecting a specific point in time from the prospective of the computer that instructs frozen image generation.
On the other hand, according to the second and third technologies, the specific point in time is when a host computer instructs the generation of frozen images and data save begins. When storing frozen images as backup data, another copy processing is required according to the second and third technologies. During this copy processing, control load becomes concentrated on the storage apparatus, which can impact response time for online programs.